devtools: Split Network.getCookies into Network.get{All,}Cookies

This patch splits the Network.getCookies command into
Network.getCookies, which returns the cookies for the current URL and
Network.getAllCookies, which returns all the cookies in the cookie jar.

BUG=668932,166637

Review-Url: https://codereview.chromium.org/2568503002
Cr-Commit-Position: refs/heads/master@{#438198}
7 files changed